This paper reviews some scientific considerations about the underlying material properties and the detailed functional principle of two important types of solid state gas sensors. This is used to predict the application potential of these sensor technologies. The classical methodology to use resistance readout of heated semiconducting metal oxides is a straightforward approach to get robust sensors that are simple in design. The usage of materials that are operated at higher temperatures opens up the way for improvements; due to a change in the mechanism of electrical conductivity, better reproducibility and stability of the electrical properties can be attained. The high operation temperatures also lead to changes in the surface reactions with the gases that allow for quicker equilibration times. The next step is taken when devices are used that are based on the readout of the work function of the sensing materials. Suspended gate FETs here serve as the transducer structures. Surface properties are directly used here, which facilitates the preparation of sensing materials. The sensors can be used with a wide range of sensing materials, allowing the development of receptor materials that optimally fit the target gases. Functional improvements include enhanced selectivity and detection of a wider range of gases. These devices may work at room temperature with little energy required for running them and additionally allow direct access to the structure of the analyte molecule without thermal decomposition.