PURPOSE: To reduce the consumption of energy when a programming work is performed by a method wherein, when a programmable ROM (PROM) composed of a semiconductor is to be manufactured, the conductivity of a semiconductor layer is reduced by shifting the junction surface of the first conductive type and the second conductive type using a heat treatment.

CONSTITUTION: On the part 23 of the region 21 which was formed by a p type semiconductor, an n+ type semiconductor region 23 is formed by doping the impurities such as P, AS, Sb and the like which are in the impurity density higher than that of the p type semiconductor region 21. Then, when a heat treatment is performed at the time of programming, the boundary surface 22 of the regions 21 and 23 is shifted in the direction wherein the region 23 will be enlarged. The conductivity in the section between A and A' is high before performance of the programming, but an extremely low conductivity is indicated after the programming has been finished, because of the pnp junction formed at junctions 24 and 25. It is not absolutely necessary that the section between A and A' is completely interrupted by an n type semiconductor after the programming has been finished, and the conductivity between A and A' is reduced without fail because the area of the p type region is decreased, thereby enabling to form the PROM element having a little variation in resistance in ON and OFF states.