PURPOSE: To easily write a program by a method wherein all cell transistors are formed to be of an enhanced type, a ROM is formed, a light-shielding film is applied, an opening is formed in the light-shielding film according to a program and the whole surface of a semiconductor substrate is irradiated with light.

CONSTITUTION: A silicon film 5, a source-drain region 7 and the like are formed on a P-Si substrate, and an enhancement-type transistor is formed. Then, an Al film 8 is applied to the whole surface of the substrate by a sputtering method or the like, and an opening is former in the Al film 8 in a transistor part to be former as a depletion type according to an instructed program. Then, the P-Si substrate 1 is separated into chips, each chip is assembled in a transparent package, and an EPROM is formed. Then, the EPROM is irradiated with light, and the enhancement-type transistor is changed to a depletion-type transistor. Thereby, s program can be written easily to the ROM and the process of the method can be shortened.