A solid state compact ion gauge includes an electron source, a gate
electrode, an electron collector, a gas ionizer, an ion anode, and a
detector all formed within a cavity of a semiconductor substrate formed
of two halves bonded together and having open sides for receiving a gase
sample. A sample of gas having multiple gas constituents flows into the
cavity from the side where gas molecules collide with electrons flowing
from the source to the collector forming ions. The ions are forced under
an electric field to the detector which includes a set of detectors for
sensing the constituent ions.