The durability and reliability of segmented-in-series (SIS) type cellsstack was investigated by multimodal assessment in which Tokyo Gas collaborated with research institutes under NEDO project, "Development of system and elemental technology on SOFCs". The SIS cells-stack, developed by Tokyo Gas in cooperation with Kyocera, has many advantages such as reduced temperature operation, highvoltage / low-current power generation, and lower in material cost of electrical insulating substrate compared to Ni based substrates for anode-supported cells. Another key advantage is that there is no need for alloy interconnects. This would make the cell-stack more durable than other types of cell-stacks having metallic interconnects. Durability of the stacks was investigated by the operations in electric furnaces at Tokyo Gas, Central Research Institute of Electric Power Industry (CRIEPI), and Kyushu University. After the operations post analyses were conducted by the research institutes, such as National Institute of Advanced Industrial Science and Technology (AIST), Tohoku University, Kyoto University, The University Tokyo, and Kyushu University. Through the multimodal assessment durability and reliability of the SIS stacks for long-term operation and thermal cycles have been shown to be high enough for 40,000 h life and more.