Surface-attached hydrogel films with well-controlled chemistry are a new approach of polymer thin layers and an actual alternative to polymer brushes and layer-by-layer assemblies. The advantage is that the thickness of hydrogel films can widely range from a few nanometers to several micrometers. Hydrogel films can also remarkably respond to stimuli such as temperature: (i) the thickness change is of great amplitude, fourfold and more, which could not be reached with the geometry of polymer brushes or layer-by-layer assemblies, (ii) the time response is very short (less than 1 s), and (iii) the swelling-to-collapse transition is narrow (a small temperature change of a few degrees may be enough). Poly(N-isopropylacrylamide) (PNIPAM) is the most temperature-responsive polymer investigated with a lower critical solution temperature (LCST) of around 32 °C. However, it is relevant to have the available polymers responding to various transition temperatures with the advantage of keeping the same chemistry. Poly[oligo(ethylene glycol) methacrylate] (PEGMA) meets these specifications since its transition temperature can be finely tuned with the number of oligo ethylene glycol units, while it attractively combines biocompatibility with PEG side chains. Here, we report the synthesis and the temperature-responsive properties of poly(PEGMA) hydrogel thin films. We used a simple, versatile, and well-controlled approach through thiol-ene click reaction, the so-called cross-linking and grafting, to synthesize surface-attached poly(PEGMA) hydrogel films with various thickness. We show that the transition temperature of poly(PEGMA) hydrogel films ranges from 15 to 60 °C if the number of PEG units is from 2 to 5. This transition temperature can also be finely adjusted for hydrogel films containing copolymers or mixing homopolymers of PEGMA with a suitable ratio. Moreover, the LCST properties, swelling-to-collapse amplitude and transition temperature, are not sensitive to salt. In particular, there is no effect on the LCST properties of surface-attached poly(PEGMA) hydrogel films in phosphate saline buffer, which is promising for applications in biology such as injectable hydrogels, drug delivery systems, hydrogel-based microfluidic valves, and flow switches for biotechnologies.