This paper describes the design, construction, and performance of a single‐stage microchannel‐plate image intensifier used as a photon counting detector over the wavelength range from 1150 to ∼2000 A˚. The intensifer incorporates three high strip current (∼300 &mgr;A) microchannel plates, constructed with 12‐&mgr;‐diam channels and 15‐&mgr; center–center spacing, in a ‘‘Z’’ configuration. The use of high strip current MCPs requires gating the power supply to protect the plates from thermal runaway of the strip current. The output pulses are proximity focused onto a P‐46 phosphor screen, which is fiber‐optically coupled to a linear, self‐scanning photodiode array. Maximum frame rates for the photodiode array are ∼ 125 000 frames/s, with maximum count rates of ∼25 000 photoevents/s. The detector was placed at the focal plane of a 1‐m focal length Ebert–Fastie spectrometer and the performance characteristics of the spectrometer‐detector system were evaluated using a hollow cathode Pt lamp. The linewidths measured during this evaluation demonstrate that the spatial resolution of the detector is better than 50 &mgr;. The spectrometer‐detector system was then used to determine ion temperatures from Doppler broadened impurity lines emitted from plasmas of the Alcator C tokamak. This detector demonstrated more than an order of magnitude increase in sensitivity compared to a photon‐counting photomultiplier tube with a vibrating mirror previously used for these measurements with the same spectrometer. This permitted a determination of the central ion temperature of the Alcator C tokamak using the ‘‘forbidden’’ line of Fexiiat 1354.1 A˚ which was not detected with the previous system.