Organic electrolyte-gated transistors (OEGTs) have the benefits of low power consumption and large current modulation. Nevertheless, the electrical performance of n-type OEGTs lags far behind that of p-type OEGTs. In this study, we design a series of polymers, P(NDITEG-T) and P(NDIMTEG-T), comprising a naphthalene diimide backbone for n-type charge transport and oligo(ethylene glycol) (OEG) side chains for high ionic conductivity and eco-friendly solution processing. The incorporation of the OEG chain facilitates the electrochemical doping of the semiconductor by ions to realize high-performance, n-type OEGTs. Notably, in OEGTs, P(NDITEG-T) achieves a high electron mobility of 1.0 x 10(-1) cm(2) V-1 s(-1), which represents the highest value reported for solution-processed, n-type OEGTs. It is noted that the fabrication of the OEGTs is achieved by solution processing with eco-friendly ethanol/water mixtures in virtue of the hydrophilic OEG chains. This work demonstrates the molecular design of the P(NDITEG-T) polymer and its significant ability to produce aqueous-processable, high-performance, and n-type OEGTs.