Transparent p‐type CuI layers with high hole mobility can be fabricated on flexible plastic sheets, a system which has been unattainable with p‐type transparent oxide semiconductors. Mildly heat‐treated CuI layers have mobilities of ≈20 cm2 V−1 s−1, which are comparable to those of p‐type GaN epilayers. Highly transparent p–n diodes with sufficient rectification ratio (106) can be manufactured by employing a heterojunction of p‐type CuI and amorphous n‐type In‐Ga‐Zn‐O layers on plastic sheets. Thus, CuI can be regarded as an excellent transparent p‐type semiconductor for flexible transparent electronics.