In situ monitoring of tissue temperature during in vivo experiments can be of great advantage. It could allow the detection of inflammation development and possible infections caused by the implanted devices, the prevention of overheating due to electrical or optogenetical stimulation and the recording of effected vasodilation and increased metabolism. In this work, we present the characterization of platinum temperature sensors integrated in thin-film polyimide substrates. Three different sensor types were fabricated, with the intent to match a Pt 100, a Pt 1000 and a Pt 5000, all of them showing the typical characteristic curve of platinum for the electrical resistance as a function of temperature. Sensitivities of 0.2 Ω/°C, 1.7 Ω/°C and 8.8 Ω/°C were determined for the different sensor types. With the Pt 5000 samples temperature changes of less than 0.5 °C could be detected reliably, independent of the ambiance being air or water. Good in vivo behavior of the platinum sensors is assumed as the fabrication process was not altered compared to established polyimide-based electrode arrays.