An exhaust monitoring cup which measures exhaust gas flowing through a top opening in a coater cup of a spin coating apparatus used in the deposition of photoresist coatings on semiconductor wafers. The exhaust monitoring cup includes a gas flow cup which is positioned in fluid communication with the top opening of the coater cup. The exhaust gas flows through a gas flow opening in the gas flow cup, and a flow rate measuring apparatus at the gas flow opening receives the exhaust gas and measures the flow rate thereof. The flow rate of the gas leaving the gas flow cup can be compared to the flow rate of the gas flowing from an exhaust conduit leading from the bottom of the coater cup, to facilitate detection of abnormal conditions in the coater cup or exhaust conduit.