Semiconducting single-walled carbon nanotubes (s-SWNTs) are attractive candidates for next-generation printable semiconductors. However, all current synthesis methods produce s-SWNTs which are co-mingled with metallic (m-) SWNTs. Agarose gel electrophoresis has been reported to be an effective technique for the separation of s-SWNTs from m-SWNTs but removal of the agarose gel after separation has proved to be non-trivial. To remove agarose and the organic dispersing agent, specifically chondroitin sulfate in this work, from sorted s-SWNTs obtained by agarose gel electrophoresis, we employ the multi-step process involving a chlorosulfonic acid (HSO₃Cl) wash, a base wash and thermal annealing. Herein, we report the detailed analysis of the effects of the various steps for gel removal from SWNTs by Fourier transform infrared (FTIR) spectroscopy, thermal gravimetric analysis (TGA), FTIR-TGA, scanning electron microscopy, atomic force microscopy and Raman spectroscopy. The polymer-contaminated s-SWNTs were dissolved in HSO₃Cl, then selectively precipitated in a large excess of water, then washed with a base (NaOH) and finally thermally annealed. A detailed analysis confirmed that the final annealed samples contained almost no residual polymers. Field effect transistors were also fabricated from the annealed s-SWNTs and they showed good performance metrics with on/off ratio and mobility in the ∼10² to 10⁶ and ∼2.5–9.5 cm² V⁻¹ s⁻¹ ranges, respectively. Our method of gel electrophoresis and chlorosulfonic acid treatment produces clean and defect-free tubes which may be used for electronic applications.