One of the main difficulties foreign students experience is the acquisition of lexis. However, the problem goes beyond that issue since learners ignore or neutralize the difference between lexemes of the same semantic field that share a common core of semes. Often it occurs not just because of the wrong choice, but because of the generalization of the use of only known lexeme. The semantic field that generates more errors in the process of teaching/learning of Spanish as a foreign language is related to the choice and use of the verbs ser, estar and haber. This article is the result of the merger between the acquisition of second languages and corpus linguistics. The research data was obtained through collecting, analyzing and providing results from the compositions written in students’ blogs. A blog was used as a written genre. A blog is a transparent and simultaneous means of writing and publishing with discursive features that are converted into linguistic characteristics. These characteristics reflect the personal, informal and spontaneous nature of this genre and compile a corpus of written language and observe a variety of mistakes that students make when learning Spanish as a second language. Specifically, in this article, the mistakes they make with the verbs ser, estar and haber. In particular, we follow a methodology based on the principles of corpus linguistics in its different stages, from the collection of the corpus, its labelling (identification and classification of errors) and annotation to the extraction of the results.One of the main difficulties foreign students experience is the acquisition of lexis. However, the problem goes beyond that issue since learners ignore or neutralize the difference between lexemes of the same semantic field that share a common core of semes. Often it occurs not just because of the wrong choice, but because of the generalization of the use of only known lexeme. The semantic field that generates more errors in the process of teaching/learning of Spanish as a foreign language is related to the choice and use of the verbs ser, estar and haber. This article is the result of the merger between the acquisition of second languages and corpus linguistics. The research data was obtained through collecting, analyzing and providing results from the compositions written in students’ blogs. A blog was used as a written genre. A blog is a transparent and simultaneous means of writing and publishing with discursive features that are converted into linguistic characteristics. These characteristics reflect the personal, informal and spontaneous nature of this genre and compile a corpus of written language and observe a variety of mistakes that students make when learning Spanish as a second language. Specifically, in this article, the mistakes they make with the verbs ser, estar and haber. In particular, we follow a methodology based on the principles of corpus linguistics in its different stages, from the collection of the corpus, its labelling (identification and classification of errors) and annotation to the extraction of the results.