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Chemical effects on the conduction-band filling and band-gap renormalization in ZnO thin films doped with group-III elements (Al, Ga, and In) are investigated by means of optical and photoemission experiments and first-principles density-functional calculations. The Fermi-level position, as obtained from ultraviolet photoemission measurements, exhibits a relatively small and positive shift (about 0.4 eV) with respect to the valence band for increasing electron concentrations up to . The optical gap exhibits a much larger increase for the same concentration range and the total shift appears to be smaller for In-doped ZnO. Absorption measurements under pressure show that the pressure coefficient of the optical gap is correlated with the electron concentration in films, decreasing with increasing electron concentration. As a consequence, the contributions of band filling and band-gap renormalization to the …