A CMOS reference current source comprises two circuit branches connected in parallel between supply terminals. The first circuit branch includes a series connection of a bias current source (MP1) and a first MOS transistor (MN1) of a first conductivity type. The second circuit branch includes a series connection of a diode-connected MOS transistor (MP2) of a second conductivity type, a second MOS transistor (MN2) of the first conductivity type and a third MOS transistor (MN3) of the first conductivity type. The first MOS transistor (MN 1) of the first conductivity type has its gate connected to the drain of the third MOS transistor (MN3) of the first conductivity type. The second MOS transistor (MN2) of the first conductivity type has its gate connected to the drain of the first MOS transistor (MN1) of the first conductivity type. The third MOS transistor (MN3) the first conductivity type has its gate connected to a bias source (MN4).