The development and deployment of STEM education in every continent and country are different. An instrument to access the current situation of the application, knowledge, as well as attitude towards STEM education, is necessary. This research aimed to design and develop a valid instrument that can be used to assure the quantitative degree of attitude, knowledge, and application of STEM (AKA) by science teachers. Research data were collected from 137 Indonesian secondary school science teachers. In order to determine the validity of the scale, reliability test, exploratory factor analysis (EFA), as well as the content and face validity from experts were used. Results showed that the designed and developed AKA instrument was adequate to reliabilities and validities as well as can be used to collect data. The development of AKA instrument enables users worldwide to obtain information about the development of STEM as well as the problems and challenges faced by science teachers in the field. Further work is also suggested.