In this article, we propose single-trace side-channel attacks against lattice-based key encapsulation mechanisms (KEMs) that are the third-round candidates of the national institute of standards and technology (NIST) standardization project. Specifically, we analyze the message encoding operation in the encapsulation phase of lattice-based KEMs to obtain an ephemeral session key. We conclude that a singletrace leakage implies a whole key recovery: the experimental results realized on a ChipWhisperer UFO STM32F3 target board achieve a success rate of 100% for CRYSTALS-KYBER and SABER regardless of an optimization level and those greater than 79% for FrodoKEM. We further demonstrate that the proposed attack methodologies are not restricted to the above algorithms but are widely applicable to other NIST post-quantum cryptography (PQC) candidates, including NTRU Prime and NTRU.