1. A semiconductor integrated circuit comprising; a plurality of memory blocks capable of parallel operation; an external interface means capable of externally inputting a write data and externally outputting a read data; a read buffer capable of holding a read data read out from a memory block in response to an external-output-incapable state in which said read data cannot be externally outputted from said external interface means; and a selection means for selecting either the read data read out from said memory block or the read data read out from said read buffer and feed it to said external interface means while said external-output-incapable state is not present.