Here we report gel polymer electrolytes (GPEs) formed by the film casting of the solution containing poly(ethylene glycol) methyl ether methacrylate (PEGMA) and trimethylolpropane ethoxylate triacrylate (ETPTA) with poly(vinylidene fluoride- co-hexafluoropropylene (PVDF-HFP), followed by the thermal radical polymerization and liquid electrolyte absorption. The resulting GPEs show a semi-interpenetrating polymer network (SIPN) structure that provides film robustness which is investigated by morphological, structural, and electrochemical studies. Particularly, the GPE prepared by the composition of 98 mol% PEGMA and 2 mol% ETPTA in the presence of 40 wt% of PVDF-HFP (relative to total amount of PEGMA and ETPTA) manifests large ionic conductivity (1.46 × 10-3 S cm-1) and tensile strength (6.28 MPa at elongation at break of 156%) at a room temperature due to large uptake of the liquid electrolyte (up to 267%) and SIPN structure. We also verify that the GPE is electrochemically stable up to 4.7 V (vs. Li/Li+), suggesting it holds the great promise of a polymer electrolyte membrane for energy storages such as rechargeable batteries or supercapacitors.