Provided are a reinforcing sheet which is capable of forming a secondary mounted semiconductor device excellent in impact resistance and which is capable of enhancing efficiency of a secondary mounting process; and a method for producing a secondary mounted semiconductor device using the reinforcing sheet. The present invention provides a reinforcing sheet for reinforcing a secondary mounted semiconductor device in which a primary mounted semiconductor device with a bump electrode formed on a first main surface is electrically connected to a wiring substrate through the bump electrode, wherein the reinforcing sheet includes a base material layer, a pressure-sensitive adhesive layer, and a thermosetting resin layer in this order, and the pressure-sensitive adhesive layer has a breaking strength of 0.07 MPa or more, and a melt viscosity of 4000 Pa·s or less at 60 to 100° C.