During the past decade, engineers have studying and discussing the system identification to dramatically improve the computational efficiency. System identification is a technique, which can construct a mathematical model from observed input-output data. The main objective is to find the transfer function of the Solid State Relay (SSR); therefore, an experimental setup was needed to find the transfer function. The Pulse Width Modulation (PWM) control, which was generated using Tiva Launch pad and Code Composer Studio software, was varied between 10% and 90% duty cycle and the step size was 10%. However, the switching frequency, which was 100 Hz, was remained constant, since it has the best performance among other switching frequencies in terms of output power, total harmonic distortion (THD) and power quality. The data was collected by using k-type thermocouple, NI 9213 as a data acquisition (DAQ) and LabVIEW. MATLAB's system identification toolbox was used to generate the transfer function of the temperature measurement's data of the overall plant for each duty cycle. Furthermore, the transfer function of the SSR was found in 10%, 20%, 80%, 90% and 100%; thus, the unfound SSR transfer function of the other duty cycles are recommended to be evaluated by using different methods. The transfer functions of the overall plant were successfully validated for each duty cycle by comparing the modelling results with the experimental results. Using different load rather than the heater is recommended to be used to further validate the mathematical modelling of the SSR.