Organic electrochemical transistors (OECTs) are appealing platforms for neuromorphic computing and biosensing, as they mimic the brains functionality of interacting electronic and ionic charges. While their rise to date has attracted much attention and revealed excellent application potential, little is known about the underlying physics. This deficiency applies in particular to the pronounced hysteresis found in the transfer curves - a property which, applicable as short- or long-term memory effect, is essential for neuromorphic functionality. Here we report, to the best of our knowledge, on the first temperature-dependent measurements of OECTs, which reveal remarkable insights on multiple device features to allow a glimpse into the thermodynamics of the underlying electrochemical reaction.