A semiconductor sensor, comprising a gas-sensing device and an integrated circuit is provided. The gas-sensing device includes a substrate having a sensing area and an interconnection area in the vicinity of the sensing area, an inter-metal dielectric (IMD) layer formed above the substrate in the sensing area and in the interconnection area, and an interconnect structure formed in the interconnection area; further includes a sensing electrode, a second TiO2-patterned portion, and a second Pt-patterned portion on the second TiO2-patterned portion in the sensing area. The interconnect structure includes a tungsten layer buried in the IMD layer, wherein part of a top surface of the tungsten layer is exposed by at least a via. The interconnect structure further includes a platinum layer formed in said at least the via, a TiO2 layer formed on the IMD layer, a first TiO2-patterned portion and a first Pt-patterned portion.