A process for forming low threshold voltage P-channel MOS transistors in semiconductor integrated circuits for analog applications, said circuits including high resistivity resistors formed in a layer of polycrystalline silicon and N-channel MOS transistors having active areas which have been obtained by implantation in a P-type well, comprises the steps of,providing a first mask over both said resistors and the semiconductor regions where the low threshold voltage P-channel transistors are to be formed,doping the polycrystalline layer uncovered by said first mask,providing a second mask for protecting the resistors and the semiconductor regions where said low threshold voltage P-channel transistors are to be formed, andN+ implanting the active areas of the N-channel transistors.