A field effect transistor (10) for chemical sensing by measuring a change in a surface potential of a gate electrode (48) due to exposure to a fluid has a semiconductor substrate (12) with a trench (18,20). The trench has a first sidewall (30) and a second sidewall (32) disposed opposite the first sidewall to provide a fluid gap (50) for the fluid to be sensed. The gate electrode is disposed overlying the first sidewall of the trench, and a source region (54) and a drain region (56) are disposed in the second sidewall of the trench. A channel region (52) is disposed between the source and drain regions, and the gate electrode is disposed opposite the first channel region across the fluid gap. A heater (26) for regulating the temperature of the gate electrode is disposed in the first sidewall of the trench.