In this paper, the temperature dependence of single event upset (SEU) cross-section in 28 nm embedded Static Random Access Memory (SRAM) of System in Package (SiP) was investigated. An atmospheric neutron beam with an energy range of MeV~GeV was utilized. The SEU cross-section increased by 39.8% when the temperature increased from 296 K to 382 K. Further Technology Computer Aided Design (TCAD) simulation results show that the temperature has a weak impact on the peak pulse current, which is mainly caused by the change of bipolar amplification effect with temperature. As the temperature increases, the critical charge of the device decreases by about 4.8%. The impact of temperature on the SEU cross-section is determined competitively by the peak pulse current and the critical charge. The impact of temperature on critical charge is expected to become more severe as the feature size is further advanced.