A method for producing semiconductor devices by mounting semiconductor chips 12 on a substrate 20 and resin-encapsulated the same is provided, wherein a plurality of semiconductor devices having a high reliability are simultaneously and efficiently obtained from a single large-sized substrate, comprising the steps of mounting a plurality of semiconductor chips 12 on the large-sized substrate 20 in correspondence to a plurality of unit substrates 20a formed thereon; resin-encapsulating the semiconductor chips 12 by filling a encapsulating resin 16 in the inside of the outer peripheral edge of the large-sized substrate 20; and cutting the large-sized substrate 20 thus resin-encapsulated together with the encapsulating resin 16 into individual unit substrates to obtain a plurality of resin-encapsulated semiconductor devices.