Phase‐engineered type‐II metal–selenide heterostructures are demonstrated by directly selenizing indium‐tin oxide to form multimetal selenides in a single step. The utilization of a plasma system to assist the selenization facilitates a low‐temperature process, which results in large‐area films with high uniformity. Compared to single‐metal–selenide‐based photodetectors, the multimetal–selenide photodetectors exhibit obviously improved performance, which can be attributed to the Schottky contact at the interface for tuning the carrier transport, as well as the type‐II heterostructure that is beneficial for the separation of the electron–hole pairs. The multimetal–selenide photodetectors exhibit a response to light over a broad spectrum from UV to visible light with a high responsivity of 0.8 A W−1 and an on/off current ratio of up to 102. Interestingly, all‐transparent photodetectors are successfully produced in this work. Moreover, the possibility of fabricating devices on flexible substrates is also demonstrated with sustainable performance, high strain tolerance, and high durability during bending tests. Phase‐engineered type‐II metal–selenide heterostructures are demonstrated by directly selenizing indium‐tin oxide to form multimetal selenides in a single step. The multimetal–selenide photodetectors exhibit obviously improved performance, which can be attributed to the Schottky contact at the interface for tuning the carrier transport, as well as the type‐II heterostructure that is beneficial for the separation of the electron–hole pairs.