People for long term exposed to an air-conditioned but highly humid environment are vulnerable to hyper-sensitivity or asthma triggered by fungi or dust mites. This thesis aims to develop a high-linearity and low-hysteresis capacitive relative humidity (RH) microsensor to more precisely accommodate the humidity of living spaces. To reduce the hysteresis and enhance the linearity, this research uses not only one polyimide (PI) thin film as a humidity sensing layer but also utilizes another PI thin film as a protecting layer of the top electrodes. To improve further the RH sensitivity and responding speed, interlacing out-of-plane electrodes are designed in the RH microsensor. The main processing steps of the RH sensor developed in this study involve at least five photolithographic and four thin film deposition processes. The influences of sensing area, number of electrode pairs and testing temperature on the sensitivity and sensing linearity of humidity microsensors were investigated. Based on the measurement results, the sensitivity apparently increase as well as the sensing area (2 mm ¡Ñ 2 mm: 0.12 pF/%RH, 3 mm ¡Ñ 3 mm: 0.48 pF/%RH, 5 mm ¡Ñ 5 mm: 1.09 pF/%RH), and decrease with the number of electrode pairs (40 pairs: 0.51 pF/%RH, 20 pairs: 0.4 pF/%RH) and increase with the testing temperature. The thesis has demonstrated that the capacitance of the RH sensor vary from the relative humidity with a very linear relationship (linearity: 98.8%~99.99%) over the range of 30~70%RH. Finally, to increase effectively the surface area and to reduce further the hysteresis, three-dimensional (3D) moisture entrances and exits were designed and a very low hysteresis value (0.5%RH) can be achieved.