Wireless sensor networks are comprised of energy constraint, battery powered small devices that sense the environment and transmit the data to the sink in order to take action according to data. Since the sensors are small energy constraint devices energy consumption is the main problem for wireless sensor networks. Energy spent during data communication is much more than spent during in-sensor computing. Most of the effort is spent on designing protocols in order to conserve energy. This paper proposes an improved version of energy efficient MAC protocol STEM by including pipelining mechanism. Results show that the proposed method overperform the original version of STEM by sustaining less delay. (C) 2010 Published by Elsevier Ltd. Selection and/or peer-review under responsibility of the Guest Editor.