This paper presents an analytical solution of steady-state heat transfer for laminar, two-dimensional, and rarefied gas flow in a semi-infinite microtube. To account for the slip-flow characteristics of microscale heat transfer, temperature jump condition at the wall has been included in the model while the fluid velocity is assumed to be constant (slug flow). The solution yields closed form expressions for fully-developed Nusselt numbers in terms of Knudsen number and Prandtl number under both isothermal and isoflux wall conditions.