Digital control of a mercury battery low‐noise dc power supply for an electron tunneling spectrometer is described. Advantages are reduced data accumulation time, fully automated spectrometer operation, and signal processing flexibility. Results are illustrated with an inelastic electron tunneling spectroscopic (IETS) study ofn‐propyltrichlorosilane [CH3–(CH2)2–Si–Cl3] adsorbed from vapor on a thin dc plasma‐grown aluminum oxide film.