GaAs bulk micromachining combined with MESFET technology has been applied to fabricate a thermoelectric microwave power sensor in a terminating load configuration. Its advantages are technological compatibility with MMIC processes combined with excellent performance: the sensitivity under normal ambient pressure is 2.02 V/W, inherent linearity over a dynamic range of 48 dB and a thermal time constant of 500 µs; maximum VSWR of 1.07 up to 26.5 GHz. Such integrated sensors can also be used in the millimetre-wave regime.