A CMOS reference voltage source comprises first and second circuit branches connected in parallel between supply terminals, so that the current in one branch is mirrored in the other, and vice versa. The first circuit branch includes a series connection of a first transistor (MP1) of a first conductivity type, a first transistor (MN1) of a second conductivity type and a second transistor (MN2) of the second conductivity type. The second circuit branch includes a series connection of a second transistor (MP2) of the first conductivity type, a third transistor (MN3) of the second conductivity type and a fourth transistor (MN4) of the second conductivity type. The reference voltage is provided at an interconnection node between the third and fourth transistors (MN3, MN4) of the second conductivity type. No resistors or bipolar devices are needed so that a standard CMOS process can be used.