Mechanical stress induced by mechanical and thermal loading on thin silicon devices breaks the devices at a certain load called the fracture or breaking strength of the device. The displacement experienced by the dies, due to bending, at fracture strength is called the fracture displacement. The strength properties of thin, bare silicon dies have already been reported. This work extends the study further to demonstrate the improvement in the fracture strength of thin silicon dies, of three different thicknesses (30, 65 and 130 μm), when integrated in flexible foil substrates. The fracture strength of the dies was measured using uniaxial (3-point-bending test) and biaxial (Ring-ball test) bending tests. Experimental results of the fracture strength of thin, bare silicon dies were in good agreement with simulation results obtained from Finite Element Analysis (FEA). Experimental results showed that there was an increase of the fracture strength up to about 190% and an increase in the curvature of bending up to about 85% when silicon dies were integrated in flexible foil substrates. This increase in the fracture strength and curvature of bending can be useful in designing and manufacturing more mechanically robust flexible electronic devices.