The gamma phase of copper(I) iodide (γ-CuI) is a p-type semiconductor with a wide bandgap (Eg ≈ 3.1 eV). Conventionally, γ-CuI thin films have been synthesized by the iodination of Cu thin layers with iodine vapor. However, γ-CuI films fabricated by this method have a rough surface and thus frosted-glass-like appearance, which make it difficult to apply this material to transparent electronics. In this paper, a simple new method is proposed for the synthesis of truly transparent p-type γ-CuI films. The chemical reaction between Cu3N thin films and solid-phase iodine at 25 ºC was found to yield highly transparent polycrystalline γ-CuI films with shiny appearance. The γ-CuI films fabricated by this method had root-mean-square roughness values of 8-12 nm, which are less than one-third of those for γ-CuI films synthesized by the conventional method. As a result, specular transmittance of >75% in the visible region was attained. An as-prepared film had a resistivity (ρ) of 3.1 × 10 -2 Ω cm, hole density (nh) of 8.9 × 10 19 cm -3 , and mobility (μ) of 2.4 cm 2 V -1 s -1 . Mild heat treatment at 100-150 ºC under an inert atmosphere was found to suppress nh and enhance μ. The heat-treated films had μ values of 9-10 cm 2 V -1 s -1 , which are comparable to those of other wide-bandgap p-type semiconductors grown epitaxially at high temperatures above 400 ºC. These findings would assist studies on applications of γ-CuI thin films in transparent electronics.