A 2-µm-thick single-crystal silicon (SCS) beam showed plastic deformation in the temperature range of 350–500 ℃. SCS beams made from a top layer of a silicon-on-insulator (SOI) wafer were first elastically buckled by a compressive force applied from the free end in the longitudinal direction. While maintaining the buckled state, the beams were heated to an elevated temperature for 1 h in air. After cooling and releasing the applied force, the residual bent profile was measured using a laser profiler. A plastic hinge was observed to appear for the beams bent in the temperature range of 350–500 ℃ but not at 300 ℃. Plasticity appeared under a large elastic strain in the range of 2–5% at the elevated environmental temperatures. Slip lines of the crystal were clearly observed at the plastically bent beam surfaces. We further demonstrated that a permanent out-of-plane deformation was obtained by applying hot air flow to a SCS film structure.