a description will be given of embodiments of the present invention , by referring to fig4 and the subsequent figures . fig4 is a diagram showing a layout of a memory cell of a first embodiment of a semiconductor memory device according to the present invention . fig5 is a diagram for explaining various symbols used to indicate a gate polysilicon layer , a gate contact layer , a source / drain contact region , a source / drain region , a well contact region , a cell frame , a p - type well region , and an n - type well region in the layout shown in fig4 . in this embodiment , the present invention is applied to a 1rw / 1r ram . the illustration of the circuit diagram of the memory cell of the 1rw / 1r ram will be omitted since the circuit diagram is the same as that of the conventional memory cell shown in fig1 . in fig4 , those parts which are the same as those corresponding parts in fig1 are designated by the same reference numerals , and a description thereof will be omitted . in this embodiment , the transistors trn 3 and trn 4 which are connected to the word line wla and the transistors trn 5 and trn 7 which are connected to the word lines wlb are arranged on the outer side of the other transistors in the cell frame , as shown in fig4 . more particularly , the transistors trn 4 and trn 5 are arranged in an upper portion in fig4 , while the transistors trn 3 and trn 7 are arranged in a lower portion in fig4 . hence , it is possible to use common sources / drains 11 and 12 with respect to the transistors trn 1 , trn 2 , trn 6 and trn 8 . in other words , the power supply sides vss ( sources 11 ) of the transistors trn 1 ; trn 2 , trn 6 and trn 8 may be used in common , and by further common use with substrate contacts ( contact regions of the p - type wells ) 13 , it is possible to reduce the number of contacts 14 to the power supply vss to one . in addition , common sources / drains 21 and 22 may be used with respect to the transistors trp 1 and trp 2 . by similarly using the power supply sides vdd ( sources 21 ) of the transistors trp 1 and trp 2 in common , and by further common use with substrate contacts ( contact regions of the n - type wells ) 23 , it is possible to reduce the number of contacts 24 to the power supply vdd to one . accordingly , the conventional concept of using a polysilicon layer to connect the gates of the transistors which are connected to the word lines as shown in fig2 is totally discarded in this embodiment . instead , this embodiments arranges the transistors trp 1 , trp 2 and trn 1 through trn 8 as shown in fig4 , so that gate polysilicon layers 31 of all of the transistors trp 1 , trp 2 and trn 1 through trn 8 extend in the same direction . as a result , this embodiment is less affected by the inconsistencies introduced during the production process of the memory cell . the present inventors conducted experiments to compare the layout of this embodiment shown in fig4 and the conventional layout shown in fig2 . it was confirmed from the results of the experiments that the area of one memory cell of this embodiment can be reduced by approximately 20 % as compared to the area of one conventional memory cell . as will be described later in conjunction with fig6 , contact regions in the cell frame can be used in common by arranging the layouts of the adjacent memory cells in a reverse arrangement with respect to both an x - axis direction and a y - axis direction . in other words , contact regions 13 , 23 and 43 of the memory cells can be used in common among a certain memory cell and adjacent memory cells arranged above , below , to the right and left of the certain memory cell . fig6 is a diagram showing a layout in which 8 adjacent memory cells are arranged around one certain memory cell having the layout shown in fig4 . in fig6 , those parts which are the same as those corresponding parts in fig4 and 5 are designated by the same reference numerals and symbols , and a description thereof will be omitted . in fig6 , however , the reference numerals of the transistors trp 1 , trp 2 and trn 1 through trn 8 are divided into upper and lower portion , such as “ tr ” and “ p 1 ”, because of the limited writing space available within the figure . as may be seen from fig6 , when the layout of the adjacent memory cells are reversed , or turned over relative to the layout of the certain memory cell with respect to both the x - axis direction an the y - axis direction , when arranging the memory cells in an array , that is , in a form of a memory cell array , it is possible to use the sources / drains and a bulk layer of substrate contacts in common among the memory cells . the bulk layer refers to a stacked structure from a substrate to a layer under a first metal layer which will be described later . in addition , by reversing the layout of the adjacent memory cells relative to the layout of the certain memory cell with respect to both the x - axis direction and the y - axis direction , it is also possible to use power lines such as the power lines vdd and vss , and signal lines such as the word lines wla and wlb , the bit lines bla and blb , xbla and xblb in common among the memory cells . in other words , the gate polysilicon layers of all of the transistors forming the memory cells are arranged to extend in the same direction in addition , the sources / drains of the transistors connected to all of the bit lines are arranged to be used in common among the certain memory cell and the adjacent memory cells located above and below in the plan view . moreover , the sources / drains of the transistors on the power supply side and the substrate contacts are used in common among the memory cells . furthermore , the substrate contacts are used in common among the certain memory cell and the adjacent memory cells located on the right and left . fig7 is a diagram showing the layout shown in fig6 in a simplified manner . fig8 is a diagram for explaining various symbols used to indicate a source / drain contact region , a gate contact region , and a normal position of the memory cell in the layout shown in fig7 . as may be seen from fig7 , the effect of reducing the area occupied by the memory cells becomes more notable as the number of memory cells in the memory cell array increases . in fig6 , it is assumed for the sake of convenience that the area of each memory cell is the area within each cell frame . however , a region actually occupied by each memory extends slightly to the outer side of each cell frame . hence , in units of the cell region which is actually occupied by each memory cell , the cell regions actually occupied by each of the memory cells overlap among the mutually adjacent cell regions according to the layout of the memory cells shown in fig6 . consequently , it is actually possible to further reduce the area of each memory cell by an amount corresponding to the overlap of the cell regions of the adjacent memory cells . fig9 is a diagram showing a layout of a memory cell of a second embodiment of the semiconductor memory device according to the present invention . fig1 is a diagram showing various symbols used to indicate a gate polysilicon layer , a gate contact layer , a source / drain contact region , a source / drain region , a well contact region , a cell frame , a p - type well region , an n - type well region , and a first metal layer of the layout shown in fig9 . in addition , fig1 is a diagram showing a layout of power lines in this embodiment . fig1 is a diagram showing various symbols used to indicate a second metal layer , a third metal layer , a first via hole , a second via hole , and a stacked via hole region in the layout shown in fig1 . in this embodiment , the present invention is also applied to a 1rw / 1r ram . the illustration of the circuit diagram of the memory cell of the 1rw / 1r ram will be omitted since the circuit diagram is the same as that of the conventional memory cell shown in fig1 . in fig9 , those parts which are the same as those corresponding parts in fig4 are designated by the same reference numerals , and a description thereof will be omitted . as may be seen from fig9 and 11 , similarly to the power line vss which is arranged between the bit lines bla and blb in the same wiring layer ( wiring level of the third metal layer ), the power lines vdd and vss are arranged between the word lines wla and wlb in the same wiring layer ( wiring level of the second metal layer ). in other words , by arranging the power line so as to be sandwiched between the signal lines in the same wiring layer , it is possible to reduce the coupling capacitance generated between the signal lines , and to prevent generation of noise and inversion ( transformation ) of data . as a result , it is possible to reduce the coupling capacitance between ports of the 1rw / 1r ram which is a multi - port ram , and accordingly , prevent interference between the ports . in the embodiments described above , the present invention is applied to the 1rw / 1r ram . however , the application of the present invention is not limited to the 1rw / 1r ram , and the present invention is similarly applicable to various other kinds of semiconductor memory devices . further , the present invention is not limited to these embodiments , but various variations and modifications may be made without departing from the scope of the present invention .