There is a growing trend in medicine toward minimally invasive surgery - especially in cardiovascular and intracardiac interventions - but current pull-cable based catheters lack the manipulative ability to achieve precise, complex motions. The ability to provide in situ actuation at a desired position in the body could lead to a new platform of interventional tools. In this work, we propose the concept of a laser machined SMA-based strain sensor to provide position feedback for control and manipulation of SMA actuators with nonlinear behavior. We have found that the resistance of SMA in austenite phase increases quadratically and exhibits little hysteresis below 1.2% strain. This paper presents the characteristics of our SMA sensor and its feasibility as a position sensor for feedback control of an active catheter.