Provided is a thin film vapor chamber for portable electronic devices. The vapor chamber includes: a lower plate formed in a plate shape and having protrusions formed on an upper surface thereof, first protrusions formed to protrude and formed on one side of the upper surface thereof to be spaced apart from each other, and a first joint body formed to protrude upward and formed inward from an outer edge thereof; and an upper plate formed in a shape corresponding to the lower plate and including a second joint body formed to protrude and joined to an upper side of the lower plate, second protrusions formed to correspond to the first protrusions, an inlet formed on an inner side of each of the second protrusions and into which a working fluid is injected, and a step formed to protrude downward to close the inlet by contact with the lower plate.