The invention relates to a method and apparatus for providing an electrochemical
gas sensor having improved response time for detecting a gas introduced into the
sensor. The sensor includes a substrate having a first surface and a second surface
and an electrode deposited on the first surface. The sensor also includes an ionomer
membrane in contact with the first surface and the electrode. The ionomer membrane
has an opening in a location proximate to the electrode for permitting gas introduced
into the sensor to diffuse through the opening to simultaneously contact the electrode
and the ionomer membrane within the opening. The substrate further includes at
least one hole extending from the first surface to the second surface for permitting
moisture to diffuse through the at least one hole to contact the ionomer membrane
for enhancing sensitivity.