A new technique is shown to studyinsituthe chemical composition of sputtered films. The method is based on the x‐ray emission induced by the fast electrons of the sputtering discharge. The sputtering chamber is coupled with a vacuum x‐ray spectrometer. As a demonstration of the method, the Co deposition is studied. The Co L&agr;x‐ray line and the deposition rate (by means of a quartz microbalance) are recorded as a function of time. X‐ray intensity increases quickly during the first minutes of the deposition, then levels off gradually while the deposition rate remains constant. It is speculated that a fraction of a monolayer should be detectable.