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We report on the fabrication and characterization of vertical-geometry transparent-Schottky-barrier photodetectors based on ZnSe and ZnMgBeSe structures grown on GaAs substrates. These detectors operate in the blue and ultraviolet spectral range. A responsivity as high as 0.12 A/W has been obtained at 460 nm with a sharp cutoff and a rejection rate of 5 × 103. A linear variation of the photocurrent versus the incident optical power has been measured which proves the absence of an internal gain mechanism. Wavelength cutoffs can be tuned from 460 to 415 nm by increasing Mg and Be contents. Very low dark current levels have been obtained thanks to the growth of ZnMgBeSe structures lattice matched onto GaAs substrates.