temperature higher than the reference temperature the second n type field effect transistor 140 has a greater fractional increase within increasing temperature in on current per unit temperature change than the first n type field effect transistor 130 thus when the circuit enable transistor 150 is turned on and the ambient temperature of the devices that the third exemplary semiconductor circuit is implemented in is higher than the reference temperature the first voltage at the left internal node il is higher than the second voltage at the right internal node ir further at a temperature lower than the reference temperature the second n type field effect transistor 140 has a greater fractional decrease with decreasing temperature in on current per unit temperature change than the first n type field effect transistor 130 thus when the circuit enable transistor 150 is turned on and the ambient temperature of the devices that the third exemplary semiconductor circuit is implemented in is lower than the reference temperature the first voltage at the left internal node il is lower than the second voltage at the right internal node ir as in the first embodiment a change of sign in the difference between the first voltage and the second voltage at the input nodes of the differential amplifier 190 induces a change in the output of the differential amplifier 190 the output as an indicator of the ambient temperature of the region of a semiconductor chip in which an implementation of the first exemplary semiconductor circuit is located may then be employed as a control signal for changing behavior of other circuits for optimized performance fig4 shows an exemplary method of employing the output of the first through third exemplary semiconductor circuits for adjusting operation of devices in.