Disclosed are a method of monitoring a semiconductor device fabrication process and a method of fabricating a semiconductor device using the same. The monitoring method may include determining a normalization range of a target byproduct, which is a measurement target of byproducts produced in a chamber by an etching process, the byproducts including the target byproduct and a non-target byproduct, the target byproduct including first and second target byproducts, which are respectively produced by and before the etching process on a to-be-processed layer, obtaining a first index from a ratio of the target byproduct to the non-target byproduct, obtaining a second index by subtracting an emission intensity of the second target byproduct from the first index, obtaining a third index by integrating the second index on a time interval, and estimating a result of the etching process and presence or absence of a failure, based on the third index.