A high intensity focused ultrasound transducer includes an ultrasonic emitter having a surface that emits ultrasonic energy along a beam path, at least one low attenuation polymeric ultrasonic lens acoustically coupled to the surface in the beam path of the ultrasonic energy, such that the lens can direct the ultrasonic energy in at least one direction, and at least one stress mitigation feature, such as a kerf, a heat sink, or an acoustic matching layer, to mitigate thermal expansion mismatch stresses within the transducer. For manufacturing simplicity, the first surface is typically either flat or monotonically curvilinear. The lens may take a variety of shapes, including Fresnel features, and may focus, collimate, or defocus the ultrasonic energy. Any orientation and positioning of the at least one ultrasonic lens relative to the first ultrasonic emitter is contemplated. Manufacture is further simplified by molding, casting, or thermoforming the lens.