Location-based routing for Mobile Ad hoc Networks (MANETs) use location information in routing decisions. However, location-based routing protocols need location services to query the location information of the communication partner node so that packets could be forwarded properly. In this paper, we propose a proactive flooding-based location service which named Semi-Flooding Location Service (SFLS). The basic design issue in our proposal is to minimize the number of update packets sent over the whole network. We employed a conditional update technique that manages the number of the updates at the forwarder nodes. This way reduces significantly the overhead of location updates. To study the effectiveness of our algorithm, a mathematical model is developed, and some numerical results are generated. Results demonstrated that SFLS achieves its design goals.