Future earth observation optical systems will be more and more demanding in terms of ground sampling distance, swath width, number of spectral bands, duty cycle. Existing architectures of focal planes and video processing electronics are hardly compatible with these new requirements: electronic functions are splitted in several units, and video processing is limited to frequencies around 5 MHz in order to fulfil the radiometric requirements expected for high performance image quality systems. This frequency limitation induces a high number of video chains operated in parallel to process the huge amount of pixels at focal plane output, and leads to unacceptable mass and power consumption budgets. Furthermore, splitting the detection electronics functions into several units (at least one for the focal plane and proximity electronics, and one for the video processing functions) does not optimize the production costs : specific development efforts must be performed on critical analog electronics at each equipment level and operations of assembly, integration and tests are duplicated at equipment and subsystem levels. Taking into account these constraints, Alcatel Space has developed with CNES a new concept of Highly Integrated Detection Electronic Subsystem (SEDHI). This paper presents the design of this new concept and summarizes the main performances which have been measured at component and subsystem levels. The electrical, mechanical and thermal aspects of the SEDHI concept are described, including the basic technologies : ASIC for detector clocks driving, ASIC for video processing, ASIC for phase trimming, hybrids, microchip modules... The adaptability to a large amount of missions and optical instruments is also discussed. Design, performance and budgets of the subsystem are given for the Pléiades mission (successor of SPOT) for which the SEDHI concept has been selected.