Electrothermal analogy allows heat conduction and heat convection to be modeled as a simple resistive or RC network. A practical environment in which a chip is located is often not purely convective. Nonetheless, the environment is typically approximated as convective for simplicity of analysis. This yields inaccuracy of temperature estimation; ad hoc calibration process is necessary to match estimation and measurement by empirically adjusting thermal parameters. In this brief: 1) we extract electrothermal analogy through mathematical derivation and 2) this allows us to understand how the basic resistive network can be modified to handle non-convective environment accurately. The new network is applied in the estimation of steady-state and transient temperature as well as in thermal design power. A smartphone under the sunlight is assumed as an example of non-convective environment. Estimation of steady-state temperature using our network is compared to actual measurement, which demonstrates its accuracy.