In this study, a temperature measurement was performed by determining the linear slope in the transmission spectrum of fiber Bragg grating (FBG) and by designing a temperature measurement system with the density fluctuation of a stationary continuous wave (CW) laser light on this line. The measuring range, which may change depending on the transmission spectrum of the FBG, was determined to be 12°C for this study and measurements were performed with 0.06°C accuracy. Gaussian fitting with negligible time loss and high noise immunity increased the signal‐to‐noise ratio (SNR) ratio to 37.5 dB. A simple, cost‐ efficient, high‐speed, and high SNR, ergonomic, compact temperature measurement system was created with the suggested slope technique and by using a very limited number of fiber optic components.