Abstract: A semiconductor integrated circuit such as an MOS random access memory or RAM is made by standard N-channel silicon gate manufacturing methods but using positive photoresist for successive masking steps by re-exposure of the photoresist. In making ion implants for threshold adjustment, the positive photoresist is deposited and exposed using a first mask which defines the channel areas of transistors which are to have one threshold voltage; upon developing, the channel areas will be bare so a first implant will penetrate only these channel areas. Then, without stripping the photoresist, another exposure using a second mask defines the channel areas of transistors which are to have another threshold voltage. After the photoresist is developed a second time, another implant will penetrate the channel areas defined by the second mask as well as the first.