A number of micromachined devices including a micromachined pump for on-chip vacuum is provided. For example, a single-chip micromachined implementation of a Knudsen pump having one or more stages and which uses the principle of thermal transpiration with no moving parts is provided. A six-mask microfabrication process to fabricate the pump using a glass substrate and silicon wafer is shown. The Knudsen pump and two integrated pressure sensors occupy an area of 1.5 mm.times.2 mm. Measurements show that while operating in standard laboratory conditions, this device can evacuate a cavity to 0.46 atm using 80 mW input power. High thermal isolation is obtained between a polysilicon heater of the pump and the rest of the device.