Sometimes it can boost the value of the shares but that is far from a rule. Often after a stock undergoes a long run higher, a stock split, particularly if it is 3:1, 4:1 or more, will occur very close to the ultimate end of the run for the stock (see tech stocks in late 1999 / 2000 as just one example.) The stock split is just one factor, and a relatively minor one at that, to consider when evaluating a stock.