Metal oxide semiconductors are interesting for next-generation flexible and transparent electronics because of their performance and reliability. Tin dioxide (SnO) is a very promising material that has already found applications in sensing, photovoltaics, optoelectronics, and batteries. In this work, we report on electrolyte-gated, solution-processed polycrystalline SnO transistors on both rigid and flexible substrates. For the transistor channel, we used both unpatterned and patterned SnO films. Since decreasing the SnO area in contact with the electrolyte increases the charge-carrier density, patterned transistors operate in the depletion mode, whereas unpatterned ones operate in the enhancement mode. We also fabricated flexible SnO transistors that operate in the enhancement mode that can withstand moderate mechanical bending.