Poly (ethylene glycol)-based urethane (PEG-PU) was introduced as a rubbery material to enhance mechanical properties of thermo-responsive cross-linked poly (N-isopropylacrylamide) (PNiPAAm) hydrogel by IPN formation technique. Semi-IPN hydrogels were synthesized with the ratio of PNiPAAm to PEG-PU (100/0, 95/5, 90/10, and 80/20). The various swelling or/and-deswelling behaviors were examined as a function of temperature. The volume phase transition temperatures (T_p) of semi-IPN hydrogels were little affected by the incorporation of PEG-PU chains in IPN structures. This observation indicates that each network in the swollen IPNs exists independently. The faster swelling-deswelling kinetics of semi-IPN hydrogels was observed via introduction of PEG-PU in IPNs in contrast to the pure PNiPAAm gel. These results were interpreted as a formation of water release channels within the skin layer by the hydrophilic PEG-PU chain.