Semi-insulating GaN(Fe) films grown by molecular beam epitaxy (MBE) were characterized by measuring electrical properties, deep-level spectra, Fe distribution profiles, microcathodoluminescence (MCL) spectra, electron-beam-induced current, and MCL imaging. The films were high-quality GaN(Fe) with Fe concentration from similar to 3 x 10(16) to similar to 3 x 10(17) cm(-3). The resistivity of GaN(Fe) buffers was > 10(5) Omega cm, with the Fermi level pinned near E-c 0.5 eV. The buffer quality was characterized for Si-doped GaN and AlGaN/GaN transistor structures grown by MBE on GaN(Fe). In contrast to the reported results for growth by metallorganic chemical vapor deposition, Fe distribution profiles did not show long tails extending into the layers grown on top of GaN(Fe). No features attributed to Fe were observed in lightly doped n-GaN grown on GaN(Fe) buffers. The n-GaN films showed electron mobility of > 500 cm(2)/V s. AlGaN/GaN transistor structures grown on GaN(Fe) buffers showed two-dimensional electron gas mobility > 1900 cm(2)/V s at 300 K, with a sheet density similar to 1 x 10(13) cm(-2) and a good pinch-off and a low interdevice leakage. (c) 2007 The Electrochemical Society.