We report a new crosslinked polyvinyl alcohol (PVA) layer to protect organic thin-film transistors (OTFTs) using the glutaraldehyde (GA) as a crosslinking agent. After thermal crosslinking reaction of PVA with GA, the water contact angle was increased from 9.8 degrees to 55.1 degrees as more hydrophobic state. This clearly means that hydroxyl group of PVA surface was disappeared by the crosslinking reaction. Thermally crosslinked PVA/GA was successfully adapted as solution processable passivation layer for pentacene TFT. In case of well known photo-crosslinked PVA/ammonium dichromate (ADC) passivation, extremely large initial performance drop (almost 52% mobility drop) was observed after passivation. PVA/GA passivation, however, only 3.8% initial mobility drop was found after passivation process. In addition, pentacene TFT with PVA/GA passivation layer exhibited very stable TFT operation with almost no field effect mobility drop or threshold voltage shift up to 1100h.