Overexpression/amplification of erb-b2 receptor tyrosine kinase 2 (ERBB2) is a major prognostic factor in gastroesophageal cancers; it is currently the only biomarker established for the selection of targeted therapy for patients with advanced gastroesophageal adenocarcinoma (GEA). Current standard procedure for determining ERBB2 status in such patients is immunohistochemistry (IHC), followed by in situ hybridization (ISH), when IHC result is equivocal. Insufficient knowledge regarding the utilities of chromosomal microarray (CMA) has hindered its use as an adjunct tool in ERBB2 analysis. Here, we performed CMA on 7 formalin-fixed paraffin-embedded (FFPE) GEA specimens previously tested by ERBB2 fluorescence in situ hybridization (FISH) and evaluated the concordance and performance of CMA. CMA identified 4 (57.1%) samples with amplification of ERBB2, compared to 3 (42.9%) by FISH. CMA also detected several additional DNA copy number variants in these samples, which may have prognostic and therapeutic indications. Further case studies and clinical trials may provide evidence for the utility of CMA-based genomic studies in the management of patients with suspected ERBB2-positive gastroesophageal adenocarcinoma.