Abstract: The present invention provides methods and systems for forming deposition films on semiconductor wafers. In particular, the present invention measures the amount of liquid remaining in a bubbler ampule of a semiconductor processing system used for chemical vapor deposition (CVD) on a semiconductor wafer. More particularly, measurements are made when gas has stopped flowing through the ampule, and the liquid is in a static condition. The system of the present invention comprises a container containing a liquid, a gas inlet for introduction of gas into the liquid, a gas outlet, and a pressure transducer fluidly connected to the gas inlet and the gas outlet. The device measures the amount of liquid in a bubbler ampule through measurements of gas pressure differential between gas exiting a nozzle near the bottom of the liquid and gas located above the level of the liquid. The depth of liquid remaining in the ampule may be extrapolated from the measured pressure differential.