A one time programmable memory including a substrate, a plurality of isolation structures, a first transistor, and a second transistor is provided. The isolation structures are disposed in the substrate for defining an active area. A recess is formed on each of the isolation structures so that the top surface of the isolation structure is lower than that of the substrate. The first transistor is disposed on the active area of the substrate and is extended to the sidewall of the recess. The gate of the first transistor is a select gate. The second transistor is disposed on the active area of the substrate and is connected to the first transistor in series. The gate of the second transistor is a floating gate which is disposed across the substrate between the isolation structures in blocks and is extended to the sidewall of the recess.