The performance of a large-aperture high-concentration parabolic trough concentrator (PTC) with a semi-circular absorber tube (AT) can be improved through external fins. However, deformation of the AT at high temperatures is of major concern. Here, an innovative design using a beam at the bottom of the AT is proposed to reduce deflection and enhance heat transfer. Using numerical models, it was shown that the deflection could be reduced by 4% and thermal efficiency of the PTC by 0.2% using an optimal beam with 10 mm height. The average surface temperature of the AT surface was decreased by 1 K. The heat transfer enhancement was due to increased convective heat transfer area including no secondary flow. The increasing thermal resistance with increasing beam height offset the benefit so that the thermal efficiency improvement remains in practice constant over the studied range (10–30 mm) of beam heights. The beam can easily be incorporated into the AT without any material change needed.