Wireless sensor networks (WSNs) have recently received growing attention as they have great potential for many distributed applications in different scenarios. Whatever the scenario, most WSNs are actually connected to an external network, through which sensed information are passed to the Internet and control messages can reach the WSN. This paper presents WISeMid, a middleware that focuses on integrating Internet and WSN at service level instead of integrating protocol stacks and/or mapping logical addresses. WISeMid allows the integration of WSN and Internet services by providing transparency of access, location and technology. To validate WISeMid, some results of a power consumption evaluation of the middleware are presented.