The channel conductance of nchannel m.o.s. transistors was measured as a function of gate voltage in the temperature range 100–450°K. From the variation of the gate threshold voltage with temperature, the density of surface states is calculated. The influence of the bulk depletion charge is taken into account. For the measured samples, the density of surface states is shown to be very small. From this fact it is concluded that the slope of the conductance is a correct measure of the mobility of the electrons in the channel.