Abstract: A semiconductor memory cell for a programmable read-only memory includes a polysilicon layer formed with laterally spaced surface regions which differ in impurity concentration and which form two back-to-back series diodes functioning as a programmable diode and an isolating diode. Because of the different impurity concentration, the diodes have different reverse-bias breakdown voltages. The programmable diode has the lower reverse-bias breakdown voltage. The high reverse-bias breakdown voltage of the isolating diode has the effect of blocking the parasitic current drain on the programming current.