Recently, automated neural architecture search (NAS) emerges as the default technique to find a state-of-the-art (SOTA) convolutional neural network (CNN) architecture with higher accuracy than manually designed architectures for image classification. In this article, we present a fast hardware-aware NAS methodology, called S3NAS, reflecting the latest research results. It consists of three steps: 1) supernet design; 2) Single-Path NAS for fast architecture exploration; and 3) scaling and post-processing. In the first step, we design a supernet, superset of candidate networks with two features: one is to allow stages to have a different number of blocks, and the other is to enable blocks to have parallel layers of different kernel sizes (MixConv). Next, we perform a differential search by extending the Single-Path NAS technique to support the MixConv layer and to add a latency-aware loss term to reduce the hyperparameter search overhead. Finally, we use compound scaling to scale up the network maximally within the latency constraint. In addition, we add squeeze-and-excitation (SE) blocks and h-swish activation functions if beneficial in the post-processing step. Experiments with the proposed methodology on four different hardware platforms demonstrate the effectiveness of the proposed methodology. It is capable of finding networks with better latency–accuracy tradeoff than SOTA networks, and the network search can be done within 4 h using TPUv3.