In this paper, we propose a control method for stable grasp of dual-fingered robots with rigid hemispherical fingertips. The main contribution of the proposed approach is to lower the probability of the object slipping out of the fingertips as optimizing the angle of the grasping force. In addition, since the controller is allowed to use the tactile sensor, the shape of an object is not limited, as long as the contact point is positioned on the vicinity of smooth curvatures. We prove the stability analysis of the proposed controller via the Lyapunov direct method. Finally, we present simulation results to validate the effectiveness of the proposed approach.