Analytical solutions for temperature distributions, heat transfer coefficients, and Nusselt numbers of steady electroosmotic flows are obtained for two-dimensional straight microchannels. This analysis is based on an infinitesimal electric double layer in which flow velocity becomes "plug-like", except very close to the wall. Both constant surface temperature and constant surface heat flux conditions are considered in this study. Separation of variables technique is applied to obtain analytical solutions of temperature distributions from the energy equation of electroosmotically driven flows. The thermal analysis considers interaction among inertial, diffusive and Joule heating terms in order to obtain thermally developing behavior of electroosmotic flows. Heat transfer characteristics are presented for low Reynolds number microflows where the viscous and electric field terms are very dominant. For the parameter range studied here (Re less than or equal to 0.7), the Nusselt number is independent of the thermal Peclet number, except in the thermally developing region. Analytical results for cases with and without Joule heating are also compared with the existing heat transfer results, and an excellent agreement is obtained between them. (C) 2004 Elsevier Ltd. All rights reserved.